The subject of the present invention is a pump or infusing medical liquids.
These days, intravenous infusion is an essential treatment technique for severe illnesses, such as cancer for example.
The effectiveness of the treatments is directly connected to the prescribed doses and limited by the level of toxicity of the active principles. The precision of the injection is therefore an important criterion when choosing what equipment to use. Furthermore, it has been observed that, in order to respect the patient's biological patterns, an active principle should, as a preference, be injected at certain times of the day, it being possible for the rate of injection to vary throughout the period of injection in order to take into account the immediate effects that the active principle has on the organism.
Moreover, it has been observed that it was possible, and even advantageous, to combine a number of products, some of which can be injected simultaneously using the same catheter, and others injected by different routes.
One trend in modern-day medicine is the move towards treatment in the patient's own home, this being more particularly true as regards difficult pathologies such as treatment for cancer and for AIDS, which require a great deal of technology in a hospital environment and follow-up treatment at the patient's home.
Most infusion equipment currently available on the market does not take account of this trend towards care in the patient's own home. Existing portable pumps are generally heavy, cumbersome and have limited autonomy. The pumps most commonly used are peristaltic pumps, which crush a polymer or silicone tube in order to convey the product from a reservoir to the catheter feeding into the patient.
This type of apparatus has the drawback of combining technical solutions which are bulky and heavy:
To crush the tube requires a great deal of force which is obtained by a cumbersome and heavy system of rollers. The motor has to be rated to be capable of obtaining these crushing forces, and this leads to a high weight. As the power consumption of the motor is high, the motor has to be powered by a series of voluminous and heavy cells or batteries, and this is in conflict with the very idea of the pump being portable.
Another solution consists in using devices of the syringe-pusher type, in which the plunger of a syringe containing the product to be injected is driven by a stepping motor. Aside from the weight and bulk drawbacks described earlier, a system of this kind cannot generally be programmed, and is suitable only for infusing a limited volume of liquid.
Document FR-A-2,689,014 in the name of the Applicant Company describes a pump for infusing medical liquids, which has a number of ducts, that is to say can allow simultaneous infusion of a number of medical liquids, with the possibility of mixing or of not mixing these liquids within the pump, which has a very small bulk and a low weight while at the same time allowing a great deal of accuracy on the flow rate over a very broad range of flow rates which can vary, for example, from between 1 milliliter per day to 300 milliliters per hour, and which offers the patient a great deal of safety.
The pump described in this document, of the type comprising at least one cylinder and piston device for drawing up a liquid from a container and delivering this liquid into a tube connected to the patient, is characterized in that it comprises:
a first piece in which there is made at least one metering cylinder which, containing a piston which is moved back and forth, opens into one of the faces of the piece, perpendicular to this face, PA1 a second piece which, resting against the face of the first piece into which each cylinder opens, comprises, opposite each cylinder, a cavity with a diameter that is greater than that of the corresponding cylinder and communicating with a liquid-supply container, PA1 and a leaktight and elastically deformable membrane closing off the opposite end of the cylinder to the piston, and the other face of which is on the side towards which the liquid is conveyed from a container, this membrane comprising at least one opening for the passage of the liquid and allowing the cylinder to be supplied with liquid as the piston moves in a direction that increases the volume of the cylinder, whereas it isolates the cylinder from the supply when the piston moves in the other direction, the liquid then being discharged from the cylinder through at least one port made therein close to the membrane.
In the known device, the metering chamber is delimited by a deformable membrane trapped between two parts of the piston, one part situated inside the metering chamber, and the other part situated outside the metering chamber. The two parts of the piston are joined together, for example by screwing, using a screw that passes through an orifice made in the membrane. This solution has the drawback that a perfect seal is not achieved between the liquid circuit and the outside. Furthermore, the piston needs to be coupled to the drive device so that it can be pulled and pushed. Since it is desirable for the motor to be removed by detaching the drive and programming part from the metering part, which is a wearing part, complex means need to be employed, for example a magnetic coupling using a ferromagnetic pellet formed in the piston. However, in addition to its complexity, this solution has the drawback that the attachment between the piston and the motor is relatively unpredictable.